1. Field of the Invention
The present invention is directed to a turbo compressor compressing gas using a centrifugal force generated by an impeller, and in particular to a motor cooling structure for a turbo compressor which is capable of implementing an effective cooling operation of a driving motor by introducing a low temperature refrigerant gas from an evaporator into a motor chamber for thereby cooling the driving motor and changing a part of a liquid state refrigerant gas into a gas state based on the heat of the driving motor during the cooling operation for the driving motor for thereby removing an accumulator which is used for changing a liquid state refrigerant gas into a gas state refrigerant.
2. Description of the Conventional Art
Generally, the compressor is a machine for compressing a gas such as air, refrigerant gas, etc. based on a rotation operation of an impeller or a rotor or a reciprocating operation of a piston and is formed of a driving force generator for driving the impeller, rotor and piston and a compression mechanism for sucking gas based on the driving force generated by the driving force generator.
The thusly constituted compressor is classified into a hermetically sealed type or a separation type based on the installed position of the driving force generator and the compression mechanism. In the hermetically sealed type compressor, the driving force generator and the compression mechanism are installed in a predetermined shaped sealed container, and in the separation type compressor, the driving force generator is installed outside the sealed container, so that the driving force generated by the driving force generator is transferred to the compression mechanism of the container.
The hermetically sealed type compressor is classified into a rotary type compressor, a reciprocating type compressor a scroll type compressor. Recently, a turbo type compressor (or centrifugal type compressor) is disclosed, which is directed to sucking gas and compressing the same using a centrifugal force generated when the impeller is rotated.
FIG. 1 illustrates the construction of a two-stage compression type turbo compressor having a Korean Patent Number 97-64567 invented by the inventor of this application. As shown therein, the conventional two stage turbo compressor includes a motor chamber 13 in which a driving motor 20 is installed at the inner center portion of a hermetically sealed container 10 for generating a driving force. A first compression chamber 11 communicating with an accumulator and a second compression chamber 12 is formed at both sides of the sealed container 10.
In addition, a gas flow path 14 is formed along an inner circumferential surface of the hermetically sealed container 10 and an outer circumferential surface of the motor chamber 13 at an inner upper portion of the sealed container 10 for communicating the first and second compression chambers 11 and 12 with the motor chamber 13. An inlet hole 13a is formed on a center lower surface of the gas flow path 14, namely, on the upper surface of the motor chamber 13, so that when the first compressed refrigerant gas flows from the first compression chamber 11 into the second compression chamber 12 through the gas flow path 14, a part of the refrigerant gas flows into the interior of the motor chamber 13 for thereby cooling the driving motor 20. An outlet hole 13b is formed so that the refrigerant gas which flowed into the motor chamber 13 through the inlet port 13a and cooled the driving motor 20 flows to the gas flow path 14 and then to the second compression chamber 12.
In addition, the driving shaft 30 mounted at the motor chamber 13 is engaged with the driving motor 20 with its both ends being inserted into the first and second compression chambers 11 and 12, respectively. First and second impellers 40 and 50 are fixed at both ends of the driving shaft 30 for sucking and compressing the refrigerant gas with its diameter in the direction that the gas is introduced being smaller than the diameter in the direction that the refrigerant gas is compressed and discharged, with its shape being conical when viewed from the driving shaft 30.
In addition, the first and second compression chambers 11 and 12 include first and second inducers (not shown) communicating with the gas flow path 14 for guiding the refrigerant gas sucked, and first and second diffusers 11a and 12a and first and second volutes 11b and 12b for changing the kinetic energy of the refrigerant gas having its pressure increased by the first and second impellers 40 and 50 to a constant energy.
A radial bearing 60 is engaged with the driving shaft 30 and the motor chamber 13 for thereby radially supporting the driving shaft 30 engaged with the driving motor 20 at both sides of the driving motor 20 engaged in the motor chamber 13. A thrust bearing 70 is fixedly engaged to the driving shaft 30 for supporting the driving shaft 30 at the outer portion of the radial bearing 60 and at the inner wall of both sides of the motor chamber 13.
In the drawings, reference numeral 10a represents a suction port, and 10b represents a discharge port.
The operation of the conventional 2-stage compression type turbo compressor will be explained with reference to the accompanying drawings.
Namely, in the conventional two-stage compression type turbo compressor, when an induction magnetic field is formed at the driving motor 20 by the electric power applied, the driving shaft 30 is rotated at a high speed by the induction magnetic force. The first and second impellers 40 and 50 fixed to both ends of the driving shaft 30 are rotated for thereby sucking the refrigerant gas from the evaporator (not shown) into the first compression chamber 11.
At this time, since the refrigerant gas sucked from the evaporator into the first compression chamber 11 has a low temperature, a part of the refrigerant gas exists in a liquid state. When the compression process is executed, the compression efficiency is significantly decreased. Therefore, an accumulator is installed between the evaporator and the first compression chamber 11 for changing the liquid state refrigerant gas into a gas state and for transmitting the same into the first compression chamber.
The refrigerant gas sucked into the first compression chamber 11 from the evaporator through the accumulator by the rotation force of the first and second impellers 40 and 50 is induced into the first inducer and then is accelerated by the first impeller 40. The thusly accelerated refrigerant gas is introduced into the first volute 11b through the first diffuser 11a and is first compressed thereby.
The first compressed gas is sucked into the second compression chamber 12 through the gas flow path 14 by the rotation force of the second impeller 50.
At this time, a part of the compressed gas sucked into the second compression chamber 12 through the gas flow path 14 flows into the interior of the motor chamber 13, in which the driving motor 20 is installed, through the inlet hole 13a formed on the lower surface of the gas flow path 14, namely, on the upper portion of the motor chamber 13, and the compressed gas cools the driving motor 20, and is discharged to the gas flow path 14 through the outlet hole 13b formed at the upper portion of the motor chamber 13 and then is combined with the first compressed gas and is sucked into the second compression chamber 12.
The first compressed gas sucked into the second compression chamber 12 by the rotation force of the second impeller 50 is induced by the second inducer and accelerated by the second impeller 50, and the thusly accelerated refrigerant gas flows into the second volute 12b through the second diffuser 12a for thereby implementing a second stage compression. The thusly second compressed refrigerant gas is discharged into the condenser (not shown) through the discharge port 10b.
In addition, since the driving shaft 30 is continuously rotated with no load during the refrigerant gas compression process, the driving shaft 30 may move either in the radial direction or the axial direction. In order to overcome the abovedescribed problem, the movement of the same in the radial and axial directions is prevented by the radial bearing 60 disposed at both sides of the driving motor 20 and the thrust bearing 70 disposed at both outer portions of the radial bearing 60.
In the conventional 2-stage compression type turbo compressor, the refrigerant gas is sucked from the evaporator into the compression chambers 11 and 12 by the centrifugal force of the impellers 40 and 50 engaged with both ends of the driving shaft 30. At this time, the driving motor 20 is cooled using the first compressed gas.
However, in the conventional 2-stage compression turbo compressor, the operation for cooling the driving motor is performed using a high temperature compressed gas which is first compressed by the first compression chamber, so that the cooling efficiency is decreased.
In addition, in the conventional 2-stage compression turbo compressor, since the refrigerant gas introduced from the evaporator into the first compression chamber has a low temperature, a part of the refrigerant gas exists in a liquid state. If the refrigerant gas which partially exists in a liquid state is directly compressed, the compression efficiency is significantly decreased. Therefore, an accumulator is additionally needed for fully changing the liquid state refrigerant gas into a gas state and then introducing the same into the first compression chamber for increasing the compression efficiency, thereby increasing the fabrication cost.